Sight for moving targets



Oct. 24, 1950 r L. MACKTA I 2,526,677

SIGHT FOR MOVING TARGETS Filed April 11, 1945 I 2 Sheets-sheaf. 1

IN V EN TOR. LEO MACKTA ATTORNEYS BY v L. MACKTA SIGHT FOR MOVINGTARGETS Oct. 24, 1950 2 Sheets-sheaf 2 Filed April 11, 1945 INVENTOR.LEO MACKTA ATTORNEYS- 1 effective range.

Patented Oct. 24, 1950 UNITED STATES PATENT OFFICE 2,526,677 SiGHT FORMOVING TARGETS Leo Mackta, Brooklyn, N. Y.

Application April 11, 1945, Serial No. 587,818 '7 Claims. (01-. 33-49)(Granted under the act, of .March a, 1883, as

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment to me ofany royalty thereon.

The invention relates to a gun sight specially,

suitable for use on guns directed against rapidly -moving targets atmoderate ranges, as involved in battle with airplanes and land vehicles.The weapon usually involved is a machine gun, pivoted for direct manualtransverse and elevation, known as a flexible gun.

In the situations which frequently develop in such actions, thenecessary lead may ultimately be found by noting the courses of tracerbullets included in the ammunition at intervals, and:-

swinging the gun accordingly. But ofttimes the variance between thegunners estimate of the necessary lead and the actual requirement,together with progressively varying requirement due to target progress,results in considerable de-,

lay in getting the fire on the target; and, indeed, in man instancesthere is a complete failure to attain accurate fire before the target isbeyond This is accompanied by great waste of ammunition, and even whenthe projectiles are gotten on the target, it is usually late in theperiod of encounter, so that effective placement is usually notaccomplished. When the encounter actually occurs, the target is at closerange and there are only four or five seconds Within which the fire of agun with the necessary quick traverse can be effective. Under theseconditions, in prior practice when the personal factors, such as goodjudgment of distance, elevation, speed, and bullet times; determinationof operation of the gun in traverse and elevation, operation of thetrigger, psychological reactions and time factors of motor reflexes,have become manifest,

there is often no possibility of accurate action of the Weapon, and thefire is purely chance hit-ormiss with a general direction toward thetarget.

It is therefore an aim of this invention to remove from the gunner theneed for basing the aim of the piece on observation of preliminary trialbursts to determine whether the necessary lead i is included in theangular relation of the bore axis to the line of sight, so that an earlyplacement of projectiles on the target may be efiected within a shortperiod of encounter, with correspondingly 1 increased chances ofplacement in vital or crippling spots on the target.

It is a specific purpose to embody a sight device with includedfunctions of such nature that, as to lead, the gunner only has to keepthe view of amended April 30, 1928; 370 0. G. 757) trolling the functionof the gun sight in a novel way.

The invention seeks also to present: a novel structure in a sight forenabling the automatic assurance of correct lead if the gunner simplymaintains the image of the target within simple stadia lines, whichconstantly movein accordance with the rate of movement of the targetacross the fieldof view in th sight device at the given range. It is aspecial purpose to provide the gunner with a device coordinated withfront and rear sights, which may be controlled from a range finder, apart of the device having an angular lateral movement at a rateaccordingto the required deflection of the gun from the line of sight,,co-

ordinated with the range and speed of the target,

so that the gunner need only'deflect thegun until a laterally movingpart in the sight remains in registry with the target in order to assurethe proper lead, after which firing may be begun.

Additional objects, advantages and features of invention reside in theconstruction, arrangement and combination of parts involved in theembodiment of the invention, as will be apparent from the followingdescription and accompanying ified mounting;

drawings wherein:

Fig. 1 is a side elevation of a gun, mount, and sight system,constructed in accordance with my invention; Fig. 2 is a front viewthereof; Fig 3 is a top view showing the gun with the bore axisat anangle to the line of sight; Y j Fig. 4 is an elevation partly insectionof a mod- Fig. 5 is a section on the line 5 5 Greg. 4;

v Fig. 6 is a rear elevation ofan elevation tracking sight mounting;

Fig. 7 is a side elevation thereof. There is illustrated a tripod mountelement Ill,

which may conform to conventional practice for a gun of the caliber andweight selected for use with my invention, and on the tripod there isfreely rotatable on a vertical axis a bracket H I having upstanding armsI2 between which a cradle i2 is pivoted on a horizontal axis forelevational movement. The cradle carries a gun l3, which may be of anyof several kinds suited to the use indicated, and is therefore onlyformally shown here, my invention being adaptable to use with theseveral kinds by suitable adaptation of the sight elements and supports.While I have shown the invention with a sight axis close above the gun,it will be clear that this is not essential and that the supportelements by which the sight elements are mounted on the gun or cradlemay be extended to permit the use of conventional magazines and shields.

The cradle includes a base bar [4, at the forward end of which anupstanding standard I5 is provided, on the upper end of which the barrell6 of the gun is pivoted for transverse movement of the breech end onthe cradle. The cradle is provided at its rear end with a horizontalsector guide rail ll concentric with the standard [5. The gun isprovided with a grip I8 on its underside, the lower end of which restsslidingly on the guide l1. The guide is grooved as at H on its rear edgeand the grip has a retainer plate l9 fixed thereon, extending downwardlybeside the guide and having an inturned flange engaged slidingly in thegroove [1' to prevent the rear part of the gun from swinging looselyupward relatively to the cradle. A trigger 20 for the gun action, may beconventionally located and operative adjacent the forward side of thegrip.

The cradle is provided with a cradle grip 2|, fixed on the rear end ofthe bar l4 and projecting somewhat toward the left and rearwardly,although it may be otherwise positioned as the construction of the gunand developed firing practice may require.

The gun pivot on the cradle includes a ring 22 pivoted on the standardl5, through which the barrel extends, but is releasably secured thereinby pins 23 inserted through the ring and into a collar 2-13 fixedpermanently on the barrel. The ring has a front sight 25 comprising anupstanding tapered rod 26 set in the upper side of the ring, at theextremity of which a sight bead is fixed, constituting the front sight25 proper in my invention.

At the rear end of the cradle a rear sight arm 2'! is fixedly mounted onthe rear end part of the bar, being bowed rearwardly to afford aclearance to permit a gunner at the rear of the gun to readily reach thegun grip I3 with one hand, and at the upper end of this arm a rear sightis mounted consisting of a ring sight 28 or other, suitable to the usesindicated. An example of alternative use not here illustrated, is thedirect sight device such as one known as the reflex sight, with orwithout the front bead 25, the reflex sight being of such function thatthe bead 25 may not be needed.

On the gun, spaced a suitable distance forwardly from the rear sight,there is mounted an upstanding bracket arm 29, on which there isrevolubly mounted a stadia disc 3!}, which in the 36 suitably mountedfixedly on the gun. A speed reduction element 31 is indicated asincluded between the motor 38 and pulley 35. Flexible electrical powerand control lead-in cables 39 are indicated, leading to the motor and amotor speed control device 40, which is formally represented. It iscontemplated that this control device will be remotely operated, or thatthe motor will be otherwise remotely controlled so that its speed willaccord with a range finding made at the remote station of control andsignal or control currents transmitted from the remote station; thesedetails being well understood, forming no novel details in thisinvention, and therefore not illustrated.

On the disc 30 there is delineated, by marking or grooving, a volutefigure, scroll or spiral 4| consisting of a continuous line beginning ator near the center of the disc and extending counterclockwise incircumvolutions of gradually increasing pitch or divergence from aconcentric direction, throughout its length. Thus at the inner part, thesuccessive convolutions are quite closely spaced, but toward the outerpart of the disc the spaces between the mutually adjacent parts of theline are successively more widely spaced, until at the outermost partthe convolutions are comparatively widely spaced.

When the gaze of a person is directed through the disc to a distantobject, and fixed so, while the disc rotates, the spiral line on thedisc will create the impression of outward or inward movement from ortoward the axis of the disc according to the direction of rotation ofthe disc; This apparent movement may be only hazily seen, due to theobservers vis'ion not being focused so near, but may be noted verydefinitely, nonetheless. It may be made more definite by including anumber of radial stationary bars 42 on the bracket 29, and these maysupport a guard ring 43 to protect the disc 30.

It is the purpose to make this apparent lateral movement of the spiralcoincide in angular rate with the angular rate of motion of a targettransverse to the direction of gaze (taking the gun pivot as the centerof these angular motions) when the movement of the spiral is notedthrough that concentric ring or zone on the discwhich is located in theline of sight when the gun is moved azimuthally to the proper angle tothe bore sight to give the necessary lead to a projectile fired duringsuch coincidence.

With the gun stationary, this simulated lateral movement of the spiralmay be in the samedirection and at the same rate as those of a targetviewed through the disc, and by having the pitch less than necessaryinwardly of the d'esiredzone on the disc and greater outwardly of suchzone, there will be coincidence of the target" movement and apparentradial movement of the scroll only when the target is seen through thelimited zone where the scroll'has theproper pitch. This';'zone may be solocated or distant from the axis ofthe disc that at the instant of. suchsight coincidence, the axis of the .gun will be at the proper angle tothe. line of sight, so thata projectile fired on the instant will reachthe projected path of .the target at the moment the target reaches theintersection. In effecting this function the spiral'must be rotated at arate proportionate to the known range and speed of the. target andremote control means. are provided to rotate the disc at speeds variableat will.

The scroll illustrated is simply suggestive and may require to be variedto fit a particular ammunition and target, but there are certainconstants affecting its form which are customarily used in computingtrajectories, and'bywhich a workable device may be embodied. Thus it isconvenient to assume a target speed of 200 miles per hour as a minimumor average speed for computations to fix on a definite pitch, and astandard ammunition for antiaircraft combat involves a known muzzlespeed of 2600 feet per second for the bullet, with a known decelerationand gravity drop. The latter and trajectory factor, or harmonization,may be disregarded in the present case.

The variation in range distances for which any sight device can beeffective is limited at a minimum short range, at which the decrease ofrange, and acceleration of relative angular rate of movement of thetarget, as well as changes of direction of the target, are so rapid anduncertain as to leave too little time for perception, mental reaction,and motor reflex action by the gunner. Consequently, at some point, hemust abandon all attempt at use of a sight, however effective, and relyon direct observation of tracer paths and reckoned or instinctive aiming0f the piece. It may be assumed for the purpose of explanation thatsomething less than 600 feet is the minimum range to be included in mysight element, and that the speed of the bullet is as above stated.

Also, as effective antiaircraft fire with small machine guns cannot withpresent ammunition be effectively carried on at ranges much over 1500yards due to deceleration of the bullet, it will be sufllcient to designthe device for ranges between 400 feet and about 1500 yards, or somewhatfurther.

On this basis, a minimum speed of rotation of the disc appropriate tothe maximum range may be used, with means to increase the speed whentargets at shorter ranges are fired on.

This speed may, for the purpose ofexemplification be arbitrarily set asone turn per second.

This rate of rotation might be chosen for a maximum range of 1000 yardsor more, but for convenience it may be assumed here that 500" yardsshall be the maximum range at which an encounter will be undertaken.

On account of the highly effective flight or flat trajectory of thebullet in the ordinary ranges of battle with airplanes and tanks, thereis not a change in the lead angle proportionate to comparatively widedifferences in range, but there is a wide variance in the rate ofmovement of the target angularly, proportionate to the range.

Thus the flight time of the bullet decreases so much as the rangedecreases, that the same or nearly the same angle of lead will beeffective on the same moving target over a substantial variation inranges, especially as experience has shown that more effective fire maybe obtained by using And there is little difference in the angle of leadfor such target when at a range of 500 yards.

At the 600 foot range, however, the plane moves at an angular rate ofabout 500 mils per second and at 400 feet moves over an angle of about700 section. At intervals it-is provided-with idler,

mils per second, and the traverse is then gov;-

erned by keeping the target in the sight and '7 manipulating the speedof thedrive to the disc manually. to maintain the lead at differentrates, and in the same zone or area of the disc in each instance or in,such other zone as required.

Thus if the disc, is rotating two and one half times per second for a600 foot range, it'would be rotated three androne half turns per secondfor a 400 foot range. At a range of 600 feet the bullet flight wouldoccupy 0.23 second, and a crossing target at the speed assumed wouldtravel approximately 69 feet or over an angle of mils. The targetmovement in one second would subtend an angle of approximately500'mils.; At 500yards range the bullet flighttime is known to .be 0.6second, the target moving in that time 1 over a distance of 180 feet oran angle of mils.

The rate v of movement of the target angularly azimuthal plane of thetarget, that portion or zone of the disc intersected by the lineof'sight at that position of the gun should have the spiralv linethereon so inclined and curved eccentrically that the spacing betweenone and the-next is 200 mils within the zone indicated representing byrotation of the scroll the rate of angular change of position of thetarget at the range of 500 yards. H

With such pitch in the particular'part of the scroll at the line ofsight, and rotating one turn per second, the intersection of theconvolutions with a horizontal radius of the disc axiswou-ld moveradially inward or outward (according to the direction of rotation) atthe rate; of. 200

mils per-second. Toward the center of the pitch should be increasedprogressively in a degree proportionate to some determined ratio betweenshorter range measurements and rates of rotation of the disc, and alsoproportionate to various target speeds at the one range. In consequence,coincidence between angular movement of the target and the apparentmovement of the scroll convolutions will occur only in that'zone of thedisc which will define the proper angle of lead when intersected by theline of sight through the center of the rear sight ring 28 and acrossthe bead 25. I

The ratio of change of pitch may be' coordinated with movements of atarget angularly when approaching on paths oblique to.the'1ine' ofsight, the inner part of decreased pitch servin'g to enable properIleadto be; maintained; when-2 the path of the ea-rget is at fangles iofless"than I 90 degrees to the line of sightJT-he outeripart of thescroll having the greatest pitch'ifw'illl :be f useful forplanes'crossing at short'distancesi or' moving at greater rates of Ispeed at 1 greater.

ranges. r v

In Figs. 4 and 5 there is shown a mounting of the disc: enablingsighting therethrough very close to its axis without obstruction by,vthe mounting or driving pulley. d

'In this instance a low hollowpedestal or foot piece 45 is formedwith acircular frarne or ring 46. thereon having a generally U-shape in crossrollers, two indicated at 41 in the upper partof 4 V disc from "Eerie jI i the pitch of.-:the spiral should be progressively less, andoutwardly of the zone referred to the the ring and one centrally locatedat its lower part. These rollers have central ribs 48 which set in adeep circumscribing groove 49 'of a mounting ring 50, supporting a disclwhich is identical with the one 30, except that it does not have anaxial mounting shaft, but is exposed to view throughout its area to thecenter. The disc is held by screws or other fastenings to an inwardlyprojected flange 52 of the ring 50. The pedestal 45 is hollow and hastwo idler pulleys 53 therein close to the ring 50 and the pedestalextends downward outwardly of these pulleys to respective openings inthe base of the pedestal. An endless cord 54 is engaged around the ring50 in the groove 49, passing inwardly around the idler pulleys 53,through the base of the pedestal and to the operating unit 36 beforedescribed.

That portion of the scroll line disc-which at any moment is apparentlymoving radially at the same angular speed as the target may beconsidered as the stadia element for the current encounter and will bedistinguished from the remainder of the scroll by its coincidence inrate of movement with the rate of movement of the image of the target,or apparent static relation to objects on the landscape.

In the use of this invention embodied as described, upon selecting atarget for encounter, the gunner sets the gun at a zero traverseposition, parallel with the bar l4, and centers the target in the sightsby rotating the cradle in azimuth and elevation so that the line ofsight passes through the centers of the ring sight 28, center of disc 38and bead 25. Then, upon receipt of a signal that the director or otherc0ntrol has made range contact-that is, that a range and target leadequivalent in rate of rotation of the disc 30 has been established, the

cradle is kept stationary on the bracket I I while.

the gun is traversed, until the angular change of position of the targetappears to be the same as the corresponding rate of apparent radialmovement of the scroll. In other words, the target appears to remain fora moment in a'stationary relation to one or more of the convolutions ofthe spiral line. Immediately then the gun is held stationary on theguide rail I! while the cradle is moved in traverse so as to maintainthe target in this relation to the scroll line, while the trigger of thegun is operated. Thereafter, pointing may be entirely or in partgoverned by observation of tracer paths, or further pointing may becontinued with entire dependence on the scroll sight.

It ma be appreciated that if traverse of the cradle is not started soonenough the target will move out of the zone of the disc 30 where the,described apparent coincidence of angular rate of the scroll andtargetexist and the scroll will then appear to have a faster or slower angularrate than the target, according to the direction of the latter.Correction can then be accomplished by moving the cradle faster orslower than required to stop the target relatively in the zone of thedisc where it was located on beginning the cradle movement, and thetarget will thereby be soon brought into agreement with the scroll ratein the proper zone. Corrections may also be made from time to time byswinging the cradle and gun as a unit so that the motion of the targetis toward the annular medial zone of the disc (between center andprimer) and then beginning tracking again as soon as fixed registry ofthe targetcand. scroll line. is again secured.

If desired a grip-released. latch or other means, not illustrated, maybe used to hold thegrip l8 or plate l9 to the sector IT releasable bygripping the grip Iain the handypreparationto adjusting the gun inazimuth 0n thecradle,

For convenience in illustrating the principle of the invention, it isshown in Figs. 1 to 5 applied to azimuth tracking only which would beuseful for instance against tanks on level terrain, or against naval.vcraft. from a land emplacement. Elevation functioning of the" inventionmay be effected by adding the necessary structure to enablecorresponding vertical adjustmen of the sight 28 around the axis 23. l 1

In Figs. 6 and 7, there is indicated a simplifie means to importautomatic elevation corrections, consisting in mounting the rear ringsight 28 on a curved bar 60 (corresponding'to thearm 21) which isconcentric with the pins 23, adjustable in a guide 6| on the frame ofthe grips 21.

This guide has a slot similarly. curved with the same center, receivingthe lower end .of the bar 60 slidably, and by means of an adjusting knob62 and the bar 69 may be adjusted-vertically in the same manner as theazimuth adjustment is secured. Thus far an approaching target, after theequivalent of range has been established in the rate of rotation of thedisc, the bar 60 is raised, while the cradle is elevated so that a lineof sight is maintained on the target and the vertical apparent movementof the scroll lines finally coincides with the vertical angular movementof the target. The bar 60 is then secured and tracking proceeded with asbefore explained. Components of both azimuth and elevation may beobtained by utilizing the two adjustments appropriately. a

I claim:

1. In a gun sighting system, a frame" mounted for movement in traverse,sighting means carried by said frame to determine a line of sight to=atarget, a gun carried-by said frame for angular movement over alimitedfrange with respectto said frame, first meansmova'blewithsjaidgun and defining a spiral rota'table.aboiitits in a plane normal tothe bore of said gun, said line of sight intersecting said spiralforallangular positions of said gun and frame, and means operable to rotatesaid firstmea'ns. 1

2. In combination, a azimuthally pivoted gun mount structure, a frontsight. thereon, a rear sight thereon, a gun azimuthally pivoted ,on themount structure, a stadia sight element thereon comprising a planiformtransparent disc mounted on the gun for rotation on the symmetrical axisof the disc, in a plane normal to the bore axis and spaced from the saidpivot of the gun, saidclisc having a scroll figure formed thereonsymmetrically with respect to said axis, and extending laterally toinclude the line of sight of the front and rear sights under leadmovement of the gun on said mount, and means to rotate the disc at apredetermined speed variable at will. v

3. The structure of claim 2 in whichs a id scroll figure hasconvolutions progressively increased in pitch from its inner part toits' outer part.

4. In a sighting system. for a gun, a" frame mounted for movement inelevation about a fiirst axis, means mounting said gun on said frame forangular move in train relatively thereto about a second axissubstantiall perpendicularto said first axis, spaced sights carried bysaid frame and defining a, line of sight parallel to the bore of saidgun in one position of the latter on said frame, means defining arotatable spiral movable as a unit with said gun and interposed acrosssaid line of sight for all angular positions of said gun relatively tosaid frame, and variable speed means connected to efiect rotation ofsaid spiraldefining means.

5. In a lead-determining system for agun, a transparent plate having aspiral comprising a plurality of convolutions delineated thereon, meansadapted to mount said plate on said gun to lie in a plane normal to thebore axis of said gun and for rotation about an axis parallel to saidbore axis, and variable speed driving means for continuously rotatingsaid plate about its said axis at a speed variable in accordance withthe range and speed of a target.

6. In a lead-determining device for a gun, a transparent disc having aspiral delineated thereon of increasing pitch from the origin outwardly,means adapted to mount said disc on a gun for rotation about an axisthrough the origin of said spiral, normal to said disc and parallel tothe bore axis of said gun, variable speed means connected to rotate saiddisc, a frame, sighting means carried by said frame and determining aline of sight fixed relatively thereto, and means adapted to pivotallymount said gun n said frame at a point spaced along the bore thereoffrom said disc.

7. In a lead-determining sight for a gun, a frame adapted to be mountedupon said gun and including a ring adapted to lie in a plane normal tothe bore axis of said gun, a transparent disc, rollers journaled atspaced points about REFERENCES CITED The following references are ofrecord in the file of this patent:

. UNITED STATES, PATENTS Number i Name Date 1,107,163 1 Grauheding Aug,11, 1914 1,127,230 Grauheding Feb.'2, 1915 1,724,093 Kauch et al. Aug.13, 1929 2,372,613 Svoboda Mar. 2'7, 1945 2,396,701 Holschuh et al. Mar,19, 1946 2,401,530 Vought June 4, 1946 2,407,191 Tear et al Sept. 3,1946 2,426,744

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